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Message-Id: <20220410214951.55294-9-Jason@zx2c4.com>
Date: Sun, 10 Apr 2022 23:49:48 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
tglx@...utronix.de, arnd@...db.de
Cc: "Jason A. Donenfeld" <Jason@...c4.com>,
Theodore Ts'o <tytso@....edu>,
Dominik Brodowski <linux@...inikbrodowski.net>,
Russell King <linux@...linux.org.uk>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
"David S . Miller" <davem@...emloft.net>,
Richard Weinberger <richard@....at>,
Anton Ivanov <anton.ivanov@...bridgegreys.com>,
Johannes Berg <johannes@...solutions.net>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H . Peter Anvin" <hpa@...or.com>, Chris Zankel <chris@...kel.net>,
Max Filippov <jcmvbkbc@...il.com>,
John Stultz <john.stultz@...aro.org>,
Stephen Boyd <sboyd@...nel.org>,
Dinh Nguyen <dinguyen@...nel.org>,
linux-arm-kernel@...ts.infradead.org,
linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
linux-riscv@...ts.infradead.org, sparclinux@...r.kernel.org,
linux-um@...ts.infradead.org, x86@...nel.org,
linux-xtensa@...ux-xtensa.org
Subject: [PATCH v2 08/11] x86: use ktime_read_raw_clock() for random_get_entropy() instead of zero
In the event that random_get_entropy() can't access a cycle counter or
similar, falling back to returning 0 is really not the best we can do.
Instead, at least calling ktime_read_raw_clock() would be preferable,
because that always needs to return _something_, even falling back to
jiffies eventually. It's not as though ktime_read_raw_clock() is super
high precision or guaranteed to be entropic, but basically anything
that's not zero all the time is better than returning zero all the time.
If CONFIG_X86_TSC=n, then it's possible that we're running on a 486 with
no RDTSC, so we only need the fallback code for that case.
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: x86@...nel.org
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
arch/x86/include/asm/tsc.h | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index 01a300a9700b..dad3027bf6a2 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -28,6 +28,16 @@ static inline cycles_t get_cycles(void)
return rdtsc();
}
+static inline unsigned long random_get_entropy(void)
+{
+#ifndef CONFIG_X86_TSC
+ if (!boot_cpu_has(X86_FEATURE_TSC))
+ return ktime_read_raw_clock();
+#endif
+ return rdtsc();
+}
+#define random_get_entropy random_get_entropy
+
extern struct system_counterval_t convert_art_to_tsc(u64 art);
extern struct system_counterval_t convert_art_ns_to_tsc(u64 art_ns);
--
2.35.1
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